1. Technical Field
The disclosure relates to a method for reporting uplink control information in a wireless communication system and a wireless communication device using the same.
2. Related Art
With continual development of wireless wideband communication network standards nowadays, a single base station may be configured to support multiple component carriers (CC) so that the overall throughput is increased. In a wireless communication system, a base station may activate a CC (for example, as a primary CC) and keep the other operational CCs deactivated. For example, for two configured CC #0 and CC #1, a base station can activate the CC #0 and keep the CC #1 deactivated.
Assuming that at a time point t1, a base station has activated a CC #0 for a user equipment (UE), then the UE needs to execute at least 3 tasks on the CC #0, such as receiving data in a downlink channel (for example, a physical downlink control channel (PDCCH) and a physical downlink shared channel (PDSCH) specified in the Third Generation Project Partnership (3GPP) standard), transmitting uplink data in an uplink channel corresponding to the downlink control information, and measuring quality (also referred to as channel state information (CSI)) of a downlink channel between the base station and the UE and reporting the CSI to the base station by using suitable resources and at a proper time. Since the CC #1 is deactivated at the time point t1, the UE does not need to execute aforementioned 3 tasks on the CC #1.
Except for the primary cell, the base station can activate or deactivate the configured secondary CCs by transmitting command messages to each UE. At a time point t2 after the time point t1, the UE receives an activation command for activating the CC #1 from the base station. The activation command may be a command message on the media access control (MAC) layer.
At the time point t2, the UE needs to execute related tasks on the CC #1, such as making a radio frequency (RF) circuit perform re-adjustment procedures corresponding to the CC #1 and making related communication protocol software to be in a ready state, so as to measure the CSI of the CC #1 after the time point t2 (step S13). At a time point t2+8 after the time point t2 (herein “8” refers to 8 unit time), the UE starts to execute aforementioned 3 tasks on the CC #1. After the time point t2+8, the base station may issue a request message to the UE to request the UE to report the CSI of the downlink channel corresponding to the CC #1. The base station can schedule downlink transmission by using the reported CSI.
In a practical implementation (for example, a 3GPP LTE system), the UE obtains the CSI of the CC #1 by measuring a channel state information-reference signal (CSI-RS) of the CC #1 and generates a corresponding CSI report according to the CSI. However, since no predetermined periodic CSI-RS is received or an RF circuit is not ready from the time point t2 to the time point t2+8, the UE cannot measure the CSI of the CC #1 or generate the corresponding CSI report. According to an existing 3GPP wireless communication standard, from the time point t2+8 to the time point t2+8+n (herein “n” units of time is the time specified by the base station for the UE to provide the CSI report), because the UE cannot successfully measure the CSI of the CC #1, it is allowed to provide an invalid CSI report to the base station.
A CSI report usually includes three main parameters: a channel quality indicator (CQI), a precoding matrix indicator (PMI), and a rank indicator (RI). The UE can set the CQI parameter to “0” in the CSI report to indicate that the CSI report is an invalid CSI report. The PMI and RI parameters are configured by a communication system with multi-input multi-output (MIMO) antenna configuration.
The CSI report can be submitted in a periodic manner or an aperiodic manner. To submit the CSI report in the periodic manner, the entire CSI report is divided into several parts and transmitted via an uplink control channel (for example, a PUCCH), and all these reported parts are integrated into the original CSI report by the base station. To submit the CSI report in the aperiodic manner, a dynamic request is issued by the base station, and the entire CSI report is transmitted to the base station all at once via an uplink shared channel (for example, a PUSCH).
During an aperiodic CSI reporting procedure, the base station requires the UE to provide a CSI report by using downlink control information. To be illustrated more clearly, the base station issues an uplink grant to the UE via a downlink control channel and requires the UE to provide a CSI report regarding a specific CC through the uplink grant, where the uplink grant indicates the physical resources in an uplink shared channel (for example, a PUSCH) to be used by the UE. Thereafter, the UE transmits uplink data via the granted uplink shared channel and provides the CSI report of the specific CC to the base station all at once via the uplink shared channel.
If the UE cannot successfully measure the CSI of the specific CC, it provides an invalid CSI report for this CC. The invalid CSI report usually occupies a lot of physical resources in the uplink shared channel. For example, in addition to uplink data, a CSI report may further include a wideband CQI of a specific CC, subband CQIs of all sub-carriers of the specific CC, a wideband PMI of the specific CC, subband PMIs of all subbands of the specific CC, and a RI value of the specific CC.